REPRODUCTIVE SYSTEM GENERALLY. 253 



brane originates an indirect influence between the parent 

 and offspring. In this the uterine arterial branches termi- 

 nate ; hence the nutrient branches which nourish the ovum 

 originate. The foetal vessels do not communicate with, 

 or even touch, those of the mother. The finest injection 

 cannot pass from one to the other ; but those of the foetus 

 run close to those of the mother, extract oxygen from them, 

 w^hich partially oxygenates the blood of the fcetus ; perfect 

 oxygenation not being required to support its dormant life. 

 The vessels pass from the foetus near to the uterine arteries 

 of the mother ; through the agency of two umbilical arte- 

 ries and a vein, that occupy a membranous rope, which, 

 when full grown, is nearly three feet in length, an inch in 

 diameter, and is called the umbilical cord ; this, in addition 

 to these vessels, gives passage also to the wachus, the whole 

 being enveloped in a reflection of the chorion. In the early 

 periods of gestation the investing foetal membranes are by 

 far the larger portion of the uterine contents ; towards the 

 middle period the foetus and membranes are nearly equal, 

 but in the latter months the weight of the young animal 

 greatly preponderates. The liquor amnii, in which the 

 foetus floats, maintains the same proportion to the placenta. 

 It remains to remark on the increase of the uterus ; which, 

 from being completely hidden W'ithin the pelvis, advances 

 its fundus beyond its cornua, nearly to the epigastrium ; 

 when at length, becoming painfully distended, it essays to 

 rid itself of its burthen by powerful contractions. 



Description of memhranes forming the placenta. — The mem- 

 branes forming the placenta are three, which, beginning the 

 description from the outside, consist of the chorion, the 

 allantoid, and the amnion. The amnion must be a mucous 

 membrane, though it is very like a serous one ; it imme- 

 diately incloses the foetus, and contains a fluid, its secretion, 

 called the liquor amnii, within which the unborn animal 

 floats. The allantoid lies between the amnion and the cho- 

 rion ; it is pecuHar for containing sacs, with which the 

 urachus communicates. These sacs are filled with the con- 

 tents of the foetal bladder, and the young one's bowels are 

 at birth always full of a yellow pultaceous mass, called 

 meconium. These things suggest that the arterialization 

 of the blood, no more in foetal than in extra uterine existence, 



